A car navigation system is one of in-vehicle systems that use disk-shaped storage media (hereinbelow referred to as a disk) that store data to perform given processes. This car navigation system functions as follows: a disk (hereinbelow referred to as a map disk) stores map data or the like; the map disk is set to a disk player; the map data or the like is read out from the map disk; and, thereby, maps displayed or routes are searched for. Furthermore, an AV (audio visual) system is another in-vehicle system using a disk. The AV system reads music data or video/sound data from a music CD or a video DVD (hereinafter referred to as an AV disk) to reproduce.
There is a case that a car navigation system and an AV system share only one disk player because of a physical setting space's limit or cost cutting, which poses a problem. Only switching disks for two purposes precludes a map disk from being continuously set. Map display or route guidance thereby becomes unpractical. Therefore, it is described that a given range of map data read out from a map disk is temporarily stored in a memory (refer to Patent Document 1). This enables such map display using the stored given range of map data even without the map disk being set in the disk player.
Patent Document 1: JP-2002-196051 A
However, temporarily storing a large range of map data is unpractical because of a memory volume limit. When a map display range or a route guidance range exceeds the stored given range of map data, the map display or the route guidance cannot continue. Consequently, re-setting the map disk in the disk player is required to read out necessary map data for the map display or the route guidance to continue.
For instance, a user needs to replace an AV disk with a map disk. When the user is a driver, it is unsafe that the driver changes the disks during driving. The driver therefore searches for a proper place to stop a vehicle. Finding the proper place is not always possible, which may causes the vehicle to exit from the stored given range of map data during searching for the place. Consequently, even a current position becomes not displayed. This significantly restricts serviceability or usability of sharing a disk player by temporarily storing a given range of map data from a map disk.